Sorry I missed this thread earlier...prolly a little late, but I spent a long weekend having some fun with train horns on my Blazer back in '07:

Blazer Train Horns

 

Don't waste your money on eBay horns. Get a Hornblasters Shocker kit from Train Horns & Train Horn Kits: Loudest Horns Available they run around $550 but it comes with everything and the horns have a lifetime warranty if they break. Check out YouTube. They throws these on the ground and hit them against things and they never break. Made out of hard ABS plastic. Or you could spend $1500 for a Nathan airchime and blow everyone away. I just took mine off my little Yaris and thinking about putting them on the blazer.